3 8o 



GENERAL BIOLOGY 



genus of plants, and many will eat only of a single species. The 

 result of the competition of the past among animals seems 

 to have been toward greater localization and concentration 

 of food supply at least for the smaller species. The flag 

 weevil (fig. 221) eats of the seeds of the blue flag (Iris ver si- 

 color) but only of the endosperm, and of that only for a 

 few weeks when it is newly formed. Likewise, carni- 

 vores, parasites and scavengers all have their peculiar 

 tastes. 



FIG. 222. Diagram illustrating lines 

 terrestrial vertebrates. 



of ecological specialization 



That these tastes may best be gratified under those condi- 

 tions that at the same time furnish the best shelter and 

 domicile for each species is a truly wonderful and altogether 

 admirable feature of their adjustment. 



Primitive terrestrial animals, recently come up from the 

 water, were doubtless "creeping things," with feet adapted 

 more for propulsion than for the support of the body 

 (fig. no, page 180). In time their descendants were able to 

 get up on their feet and walk. With better powers of loco- 



